I've been using https://www.minibits.cash/ app on GrapheneOS for my external wallet for a couple weeks. Thought I would provide an update.
Minibits is an eCash and Lightning wallet. It supports LNURL which is nice. Overall its the easiest and best eCash app I've tried. As others have mentioned I do have issues spending with NWC. But the LNURL support seems to work really well. I am guessing the NWC issues are related to their Lightning node liquidity because I often have failures with paying lightning invoices at the same time NWC payments fail.
I have a few mints set up and the CoinOS one seems to be more reliable.
Curious if others are using other NWC apps. For what its worth I have tried to set up NWC on my own node a few times now and it has been really inconsistent with Nostr apps. If I can even get it to make connections. I haven't had the time to figure it out yet.